In recent years, harmony with the global environment and decrease of the environmental load become objects in the manufacturing industry. Development of products or technologies in consideration of the environment has been speeded up. Due to a change in the external environment, even in the chemical industry, the use of compounds or heavy metal compounds with high toxicity has been independently suppressed, while there has been a movement to develop alternative technologies.
There has also been such a movement in the polyurethane industry belonging to the technical field of the present invention, and, in particular, the regulation on the use of organic tin catalyst that have been widely used as catalysts for the production of polyurethane has been strengthened in developed countries taking the lead in this movement. Therefore, development of alternative catalysts has also been actively made.
When polyurethane or polythiourethane is produced by the reaction of an isocyanate compound with an active hydrogen compound having a hydroxyl group or a mercapto group, a tertiary amine type catalyst or an organic metal type catalyst has been mainly used as a reaction catalyst. As the tertiary amine type catalyst, there have been used compounds such as triethylenediamine, N,N-dimethylethanolamine, triethylamine, N-ethylmorpholine and the like. As the organic metal type catalyst, there have been used organotin catalysts such as dibutyltin dichloride (DBC), dibutyltin dilaurate (DBTDL), dibutyltin diacetate and the like; organic acid salts and acetylacetonate complex compounds such as iron, nickel, zinc and the like. When both types of catalysts are compared, organic metal type catalysts generally have high activity, and the frequency of their use is high (Non-patent Document 1) from the viewpoint of reactivity. Furthermore, polyurethane or polythiourethane resins that have been produced by using these known catalysts have been used in various fields. Of such resins, a transparent resin made of polythiourethane belonging to the technical field of the present invention has been widely used as a plastic lens material (Patent Document 1). Since a plastic lens is lightweight and hardly broken as compared to an inorganic lens that has been used from the past, and can be tinted, in late years, it has quickly come into wide use as an optical material of spectacle lenses, camera lenses and the like.
As a catalyst to be used at the time of the production reaction of these polythiourethane resins which serve as useful optical materials, there have been widely used organotin catalysts including typical examples of DBC or DBTDL from the past from the viewpoint of high catalytic activity. However, as mentioned in the beginning, there has, in late years, been pointed out a problem in these organotin catalysts from the viewpoint of toxicity.
For example, tributyltin contained in DBTDL as impurities and tributyltin chloride contained in DBC as impurities have a problem of the risk of injury to the human body as endocrine disruptors. Furthermore, there has already been a movement of controlling use of an organic tin compound in Europe taking the lead in this movement. Therefore, in the business world of spectacle lenses using polythiourethane resins, it has been urgently desired to develop a tin substituted catalyst. From now on, not only in Europe but also throughout the world, it is highly possible that the regulation on the use of organic tin compound is still more strengthened, while, in the polyurethane industry, it becomes essential to develop a catalyst with high safety and high activity which can be a substitute of an organic tin compound.
For example, as alternatives of organic tin catalyst in the polyurethane field, there have been known a catalyst composed of a carboxylic acid metal compound and a quaternary ammonium salt compound (Patent Document 2), a catalyst composed of a two-ring tertiary amine compound and a quaternary ammonium salt compound (Patent Document 3), a metal catalyst of titanium and aluminum having an alkoxy group or a carboxy group in a ligand (Patent Document 4) and the like. These catalysts are mainly used as catalysts for the production of polyurethane resins produced from polyisocyanates and polyols. There is no case in which these catalysts are used as catalysts of polythiourethane optical materials produced from polyisocyanates and polythiols. In the field of the present invention, that is, the field of sulfur-containing plastic lenses, there has been reported a case in which dithiocarbamic acid salts of metals have been used for catalysts (Patent Document 5). However, there has not been reported a tin free catalyst which can be used for the production of polythiourethane resins that have come into wide use as materials for plastic lenses.
To produce a polythiourethane resin as a material for a plastic lens, a casting polymerization method in which a polymerizable composition is generally injected into a mold for heat curing can be taken, whereas the polymerization reaction is carried out while gradually raising the temperature from low temperature to high temperature over several hours to several tens of hours. At that time, in order to obtain an optically homogeneous plastic lens, adding a catalyst is required to slowly carry out the polythiourethanization reaction controlled by heat lest thermal inhomogeneity be occurred while raising the temperature. Furthermore, in order to achieve full resin properties including optical properties, heat resistance and strength, it is necessary to complete the polymerization. In order to complete the polymerization, a method in which a catalyst with strong polymerization activity is used or an amount of the catalyst is increased can be cited. However, such a method has a problem such that the polymerization reaction has all been progressed while the prepared polymerizable composition is injected into a mold, that is, a sufficient pot life cannot be secured. Further, there is also a problem such that during the polymerization, exothermic heat is locally generated so that optical inhomogeneity is easily exhibited to lenses. As a method to solve this problem, for example, there has been reported a case in which the low-temperature activity is suppressed by using Lewis acid for a tertiary amine with strong activity together (Patent Document 6).    Patent Document 1: Japanese Patent Publication No. 1992-58489    Patent Document 2: Japanese Patent Laid-open No. 2005-105084    Patent Document 3: Japanese Patent Laid-open No. 2005-105085    Patent Document 4: Japanese Patent Laid-open No. 2004-277621    Patent Document 5: Japanese Patent Laid-open No. 2004-269673    Patent Document 6: Japanese Patent No. 3220614    Non-patent Document 1: [Applied Technique for Latest Polyurethane] published by CMC Publishing Co., Ltd. in 1983, p. 27 to 31